The potential utility of nanoparticle solid solutions in photovoltaics has motivated several recent studies into the synthesis of these structures (Ma, 2009; Pan, 2009; Pan, 2009; Smith, 2011a; Regulacio, 2010; Maikov, 2010; Zhang, 2011; Yu, 2011; Taniguchi, 2011; Tang, 2011; Smith, 2011b). The tunability of solid solutions allows subtle variation of properties (band gap, band edge energy) to maximize device performance. This has prompted investigation of the synthesis of numerous members of the chalcopyrite and zinc blende:chalcopyrite systems (ZnS:Cu(In,Ga)(S,Se)2) (Pan, 2009a; Chen, 2011; Pan, 2009b; Zhang, 2011; Tank, 2011; Allen, 2008; Feng, 2011; Wang, 2010; Tang, 2008), (Cd,Hg)Te (Taniguchi, 2011; Yang, 2010), and Pb(S,Se,Te) (Ma, 2009; Maikov, 2010; Yu, 2011; Smith, 2011b). These studies have primarily focused on synthesis by nucleation from a solution containing a mixture of cations and/or anions, though post-synthetic treatments have also been effected (Smith, 2011a; Taniguchi, 2011; Sadtler, 2009). When particles are nucleated from a mixed-precursor solution, the kinetics of reaction often determine whether a binary or multinary compound is obtained (Chen, 2011; Tang, 2008). That is, to form Pb(S,Se), S and Se precursors must be employed that react at similar rates (Smith, 2011b). Precursor identity and solvent are particularly effective at altering reactivity. Chelating amine solvents slow reactivity of Cu+ and encourage incorporation of B into Cu(In,B)Se2 (Chen, 2011). Oleylamine has been reported to work as an “activating agent” that promotes incorporation of multiple cations (Pan, 2009; Chopra, 1983).
Bulk preparations of mixed-metal sulfides have been reported in the literature. Various forms of copper aluminum sulfide have been reported in the literature. For example, CuAlS2 (Harichandran, 2008), Cu5AlS4 (Morita, 1995), CuAlXSY. (Jeon, 2010; Jeon, 2011a; Jeon, 2011b) have been reported. Copper tin sulfides such as Cu4SnS4 are known (Girt, 2012a; Girt, 2012b; Munteanu, 2008a; Munteanu, 2008b). The copper iron sulfide, bornite, is also known (Ding, 2005; George, 2012; Grguric, 1998). However, none of these references report the preparation of mixed-metal sulfide as nanoparticles.